1. Field of the Invention
This invention relates to a method and an apparatus for electrically connecting an electrical connecting portion of a first object to an electrical connecting portion of a second object.
2. Description of the Related Art
The circuitry used in electronic parts has continued to increase in density and complexity in order to keep up with trends in size and thickness reduction of these parts. For interconnecting such electronic parts to a small-sized electrode, adhesives or film-like products, referred to below as connecting members, exhibiting superior anisotropy and electrical conductivity in order to cope with the finer pitch, are used prevalently.
The connecting members are comprised of an adhesive containing a pre-set quantity of an electrically conductive material, such as electrically conductive particles. These connecting members are provided between projecting electrodes of electronic parts and electrically conductive patterns of a printed circuit board, and are pressurized with or without heating to electrically connect the electrodes of the two components. At the same time, electrically insulating properties are afforded to the neighboring electrodes as the projecting electrode of the electronic part is secured to an electrically conductive pattern of the printed circuit board.
The basic concept for dealing with the connecting member in order to cope with the fine pitch is: 1) to select the particle size of the electrically conductive particles to be smaller than the size of the insulating portion between the neighboring electrodes to maintain insulation between the neighboring electrodes, 2) to set the content of the electrically conductive particles such as to prevent contact of the particles with one another, and 3) to cause the electrically conductive particles to be present positively on the electrodes to realize electrical conductivity in the connecting portion.
However, if, with the above-described conventional method, the electrically conductive particles are reduced in diameter, the electrically conductive particles are increased appreciably in surface area and hence undergo secondary agglomeration so that the particles cohere together. This prevents electrical insulating properties between neighboring electrodes from being maintained.
Conversely, if the content of the electrically conductive particles is decreased, the number of the electrically conductive particles on the electrodes to be interconnected is reduced so that the number of contact points is decreased. This prevents electrical conduction across the connection electrodes and renders it difficult for the connecting members to cope with the fine pitch in order to maintain long-term connection reliability.
As the electrode area or the spacing between neighboring electrodes becomes smaller with the marked tendency to fine pitch, the electrically conductive particles on the electrodes flow along with the adhesive to a gap between the neighboring electrodes under the effect of pressurization or the pressurization/heating at the time of connection to obstruct the connecting member coping with the fine pitch.
In order to solve this problem, proposals have been made for a connecting member in which an insulating coating is applied to electrically conductive particles to increase the number of the electrically conductive particles in the connecting member, and for a connecting member including an adhesive layer containing electrically conductive particles and a layer not containing the electrically conductive particles.
These conventional connecting members are shown in FIGS. 1 and 2.
Referring to FIGS. 1A-D, if an object is a glass substrate 200, having planarity in a mounting area of an integrated circuit (IC) 201 on the order of a fraction of a micrometer, and if a projecting electrode 202 of the IC 201 permits slight height variations of the projecting electrodes (on the order of a fraction of a micrometer) as in case of a gold plating bump, a wiring pattern 203 on the glass pattern 200 is electrically connected to the projecting electrode 202 of the IC 201 via electrically conductive particles 205 contained in the connecting member 204.
The reason may be summarized as follows: The parts, such as IC 201, exhibit planarity, so that, if the thickness of the connecting member 204 is on the order of the height of the projecting electrode 202 plus 5 xcexcm, the connecting member 204 is positively charged onto the lower surface of the IC 201, so that it is unnecessary to increase the thickness of the connecting member 204 to an extent more than is necessary. It is noted that the height of the projecting electrode 202 s usually 15 to 25 xcexcm, with an ITO pattern applied to the glass being a few Angstroms thick.
The ITO (indium tin oxide electrode) film is a transparent electrically conductive film affording electrical conductivity to the glass surface for operating as an electrode of a liquid crystal display plate. In an initial state of provisional pressure bonding (pressurization), the electrically conductive particles 205 can be sandwiched between the wiring pattern 203 on the glass substrate 200 and the projecting electrode 202 of the IC 201. If the binder of the connecting member flows out at the time of ultimate pressure bonding (pressurization with heating), the sandwiched electrically conductive particles 205 are not fluidized to establish positive electrical connection across the wiring pattern 203 on the glass substrate 200 and the projecting electrode 202 on the IC 201 via the electrically conductive particles 205.
FIG. 1A shows the state in which the connecting member 204, such as an anisotropic electrically conductive film (ACF), has been bonded to the glass substrate 200. The anisotropic electrically conductive film is usually bonded to the glass substrate by thermal pressure bonding (with pressurization under a pressure of 100 N/cm2 and with heating to a temperature of the order of 70 to 100xc2x0 C.). In this state, the wiring pattern 203 on the glass substrate 200 is aligned with the projecting electrode 202 on the IC 201.
FIG. 1B shows the state in which the IC 201 is provisionally pressure bonded to the glass substrate 200. The pressure bonding of the IC 201 is by pressurization only or by pressurization and heating, with the heating temperature being 70 to 100xc2x0 C.
FIG. 1C shows the state of ultimate pressurization of the IC 201 on the glass substrate 200. The IC 201 is ultimately pressure bonded under pressurization and heating. Since the heating temperature at this time is higher than the melting temperature of the anisotropic electrically conductive film, the binder is fluidized. At this time, the electrically conductive particles 205, sandwiched between the projecting electrode 202 of the IC 201 and the wiring pattern 203 of the glass substrate 200, is not fluidized, however, the other electrically conductive particles 205 are fluidized. FIG. 1D shows the cured state of the anisotropic electrically conductive film. If pressurization and heating is performed at the time of ultimate pressure bonding, the resin is first fluidized and subsequently cured. The aforementioned sequence of operations represents the connection process.
However, if, when an object is not a glass substrate, but is a printed circuit board (FIGS. 2A-D) 300, the wiring pattern 303 undergoes variations in height on the order of a few xcexcm, or the projecting electrode 202 of the IC 201 undergoes variations in height on the order of a few xcexcm, as in the case of a gold wire bump, as shown in FIGS. 2A-D. In such case, the thickness of the connecting member 204 needs to be equal to the height of the wiring pattern 303 of the printed circuit board 300 (of the order of 20 xcexcm) plus the height of the projecting electrode 202 of the IC 201 (of the order of 20 xcexcm) plus 10 to 20 xcexcm for a safety margin.
In this case, since the connecting member 204 is of an increased thickness at the stage of the initial mounting state of provisional pressure bonding (pressurization), the electrically conductive particles 205 cannot be sandwiched between the wiring pattern 303 of the printed circuit board 300 and the projecting electrode 202 of the IC 201. If then the binder of the connecting member 204 has become fluidized at the time of ultimate pressure bonding (pressurization), the electrically conductive particles 205 similarly are fluidized, such that, when the gap between the wiring pattern 303 of the printed circuit board 300 and the projecting electrode 202 of the IC 201 coincides with the size of the electrically conductive particle 205, the flowing electrically conductive particle is captured therein. However, the electrically conductive particles 205 are not involved in the entire connection, so that electrical connection cannot be achieved.
It may also be necessary to procure components with stringent specifications, thus leading to increased cost.
FIG. 2A shows the state in which a connecting member 204, such as an anisotropic electrically conductive film, has been bonded to the printed circuit board 300. The anisotropic electrically conductive film is usually bonded to the printed circuit board 300 by thermal pressure bonding (pressurization with heating), with the pressure being of the order of 100 N/cm2 and the heating temperature being of the order of 70 to 100xc2x0 C. In this state, wiring pattern 303 on the printed circuit board 300 is aligned with the projecting electrode 202 of the IC 201.
FIG. 2B shows the state of provisional pressure bonding of the IC 201 to the printed circuit board 300. The IC 201 is provisionally bonded under pressurization with or without heating, with the heating temperature being on the order of 70 to 100xc2x0 C.
FIG. 2B shows the state in which the IC 201 is provisionally pressure-bonded to the printed circuit board 300. The ultimate pressure bonding of the IC 201 is under pressurization and heating. Since the heating temperature at this time is higher than the melting temperature of the anisotropic electrically conductive film, the binder is fluidized. Since no electrically conductive particles are captured between the projecting electrode 202 of the IC 201 and the wiring pattern 303 of the printed circuit board 300, all of the electrically conductive particles are fluidized. Thus, when the gap size between the wiring pattern 303 of the printed circuit board 300 and the projecting electrode 202 of the IC 201 is equal to the particle size of the electrically conductive particle 205, the flowing electrically conductive particle 205 is captured therein. Therefore, the electrically conductive particles 205 are not present in the totality of the electrode gaps.
FIG. 2D shows the cured state of the anisotropic electrically conductive film. If pressurization and heating are effected in the ultimate pressure bonding, the resin is first fluidized and subsequently cured. This process represents the connection process. Therefore, if electrical connection via the electrically conductive particles can be made irrespective of slight irregularities on the printed circuit board in question or of slight irregularities on the projecting electrode of the IC, sufficient reliability can be achieved even with a low-cost printed circuit board.
It is therefore an object of the present invention to provide an electrical connecting member and a method for electrical connection in which an electrical connection can be reliably achieved despite slight irregularities on the objects to be interconnected.
In one aspect, the present invention provides an electric connecting device for electrically connecting an electrical connecting portion of a first object to an electrical connecting portion of a second object, including a first film-shaped adhesive layer arranged as an adhesive layer on the first object, the first film-shaped adhesive layer being composed of a plurality of electrically conductive particles and a binder containing the electrically conductive particles, and a second film-shaped adhesive layer arranged on the first film-shaped adhesive layer, the second film-shaped adhesive layer being composed only of a binder lower in melting temperature than the binder.
For electrically connecting the electrical connecting portion of the first object to the electrical connecting portion of the second object, the electric connecting device includes the first film-shaped adhesive layer containing electrically conductive particles and a second film-shaped adhesive layer formed exclusively by a binder lower in melting temperature than the binder of the first film-shaped adhesive layer.
The first film-shaped adhesive layer containing the electrically conductive particles is an adhesive layer arranged on the first object. On the adhesive layer of the first film-shaped adhesive layer is arranged the second film-shaped adhesive layer constituted exclusively by the binder lower in melting point than the binder of the first film-shaped adhesive layer.
The film-shaped adhesive layer containing the electrically conductive particles and the second film-shaped adhesive layer arranged on it are sometimes collectively referred to herein as a dual-layer film-shaped adhesive layer.
By simply arranging the dual-layer film-shaped adhesive layer on the first object, the electrical connecting portions of the first and second objects can be tightly bonded to each other by the first pressuring heating step of heating and pressuring at a temperature not higher than the melting point of the binder containing electrically conductive particles and not lower than the melting point of the binder of the overlaying layer (binder of the second film-shaped adhesive layer), despite slight irregularities on the first object, with only the binder of the second film-shaped adhesive layer being fluidized, with the electrically conductive particles of the first film-shaped adhesive layer then being not mobile. Thus, the electrical connecting portion of the first object can be positively electrically connected to the electrical connecting portion of the second object, using electrically conductive particles contained in the first film-shaped adhesive layer.
In the above electric connecting device, the electrically conductive particles are substantially of a uniform particle size, and the second film-shaped adhesive layer is an adhesive of the same or analogous quality as the binder of the first film-shaped adhesive layer.
Thus, the binder of the dual-layer film-shaped adhesive layer is reacted on pressuring and heating to bond the first and second objects together. Since the electrically conductive particles are of a substantially uniform diameter, the electrically connecting portions of the first and second objects can be electrically connected to each other without floating, as the electrically conductive particles are positively captured in-between the electrically connecting portions.
In the above electric connecting device, the thickness of the first film-shaped adhesive layer is set to be approximately equal to or larger than the diameter of the electrically conductive particles. Thus, there is no risk of the electrically conductive particles being protruded from the first film-shaped adhesive layer.
In the above electric connecting device, the viscosity of the adhesive of the second film-shaped adhesive layer is set to be lower than that of the first film-shaped adhesive layer.
The binder of the second film-shaped adhesive layer is preferentially caused to flow between the first and second objects simply by pressuring without heating. Therefore, the electrically conductive particles can be positively maintained in position, without the first film-shaped adhesive layer containing the electrically conductive particles being immobile.
In the above electric connecting device, the electrical connecting portion of the first object is a wiring pattern of a circuit substrate, while the electrical connecting portion of the second object is a projecting electrode of an electronic component. The electrically conductive particles in the adhesive layer of the first film-shaped adhesive layer electrically connect the wiring pattern of the circuit substrate to the projecting electrode of the electronic part.
This establishes positive electrical connection between the wiring pattern of the printed circuit board and the projecting electrodes of the electronic component using electrically conductive particles of the adhesive layer of the double-layer film-shaped adhesive.
In another aspect, the present invention provides an electric connecting method for electrically connecting an electrical connecting portion of a first object to an electrical connecting portion of a second object, including an adhesive layer arranging step of arranging a first film-shaped adhesive layer formed by a plurality of electrically conductive particles and a binder containing the electrically conductive particles on the electrical connecting portion of the first object and arranging a second film-shaped adhesive layer formed solely of a binder on the first film-shaped adhesive layer, and a connecting step of performing heating and pressuring for electrically connecting the electrical connecting portion of the first object to the electrical connecting portion of the second object by electrically conductive particles contained in the first film-shaped adhesive layer.
In the above method, in the adhesive layer arranging step, the first film-shaped adhesive layer, composed of plural electrically conductive particles and a binder containing plural electrically conductive particles and the second film-shaped adhesive layer is placed on the electrical connecting portion of the first object. The second film-shaped adhesive layer, composed only of the binder, is then placed on the first film-shaped adhesive layer.
In the connecting step, the electrical connecting portions of the first and second objects are electrically connected by the electrically conductive particles of the first film-shaped adhesive layer under heating and pressurization.
In this manner, if the double-layer film-shaped adhesive is arranged on the first object, the respective electrical connecting portions of the first and second objects are fluidized by the film-shaped adhesive layer becoming secured between the first and second objects. Thus, only the second film-shaped adhesive layer composed exclusively of the binder is fluidized, with the electrically conductive particles of the first film-shaped adhesive layer remaining stationary. This creates a tight bonding of the first and second objects despite certain irregularities on the first object; the electrical connection portion of the first object can be reliably electrically connected to the electrical connection portion of the second object using the electrically conductive particles of the first film-shaped adhesive layer.
In the above method, the connecting step includes a first pressuring heating step by applying pressure at a temperature not higher than the melting temperature of the binder containing the electrically conductive particles, and not lower than the melting temperature of the binder of the second film-shaped adhesive layer. The connecting step also includes a second pressuring heating step of effecting heating and pressuring at a temperature higher than the reaction starting temperature of the binder containing the electrically conductive particles and the binder of the second film-shaped adhesive layer.
In the first pressuring heating step, only provisional curing occurs, because the pressurization occurs at a temperature not higher than the melting point of the binder containing the electrically conductive particles, and not lower than the melting point of the binder of the second film-shaped adhesive layer arranged as an overlying layer.
In the second pressuring heating step, the two binders are completely cured by heating and pressurization at a temperature higher than the reaction starting temperature of the binder containing the electrically conductive particles. The binder arranged as an overlying layer (the binder of the second film-shaped adhesive layer as its sole component).
In the above method, the binder containing the electrically conductive particles and the binder of the second film-shaped adhesive layer arranged as an overlying layer are of the same or analogous components.
The present invention thus provides a way that electrical connection via electrically conductive particles can be realized positively despite slight irregularities on the object surfaces.